A semiconductor test apparatus is used to test electrical characteristics of chips fabricated on a wafer.
When fabricating semiconductor chips on a wafer are completed, the chips are tested during or after fabrication process or before packaging process for evaluating their designed electrical characteristics partially or entirely.
A probe station is one of the most popular tools for making measurements on the integrated circuits. The probe station is provided with a probe card holder for holding a probe card which applies electric signal to pads of the chips formed on the wafer.
Typically, the probe card is composed of a printed substrate and a plurality of probes mounted on the printed substrate. The printed substrate has a circuitry for electrically connecting probing devices and the probes. The probes are contacted the pads of the chips to be tested.
The wafer placed on a chuck is moved along the x-axis and y-axis to be aligned on the probe card such that the probes are positioned on the respective pads of the chips. And then, the chuck moves in z-axis such that the tips of the probes contact the pads of the chips.
The chips are tested by transmitting electrical signals generated by probe station to the tips via electric wires patterned on the printed substrate.
Recently, with the advance of semiconductor technology, device pads are arranged in various forms of arrays below a few micrometers in pitch.
As the number of parallel tests of the devices increase, the number of probes increase and, in turn, the area occupied by the device array increases, whereby alignment of the contact is becoming more critical factor for accurate contact with the pad small in size and pitch.